Switch control mechanism



March 8, 1960 E. R. PRICE SWITCH CONTROL MECHANISM Original Filed March15, 1951 7'0 PRO SL462 awn- IN V EN TOR.

5AM. E PRICE W 1:

ATTORNEY United States Patent M SWITCH CONTROL MECHANISM Earl R. Price,South Bend, Ind., assiguor to Bendix Aviation Corporation, South Bend,Ind., a corporation of Delaware 9 Claims. (Cl. 192-3) This inventionrelates in general to switch controlling means and more particularly toa power operated time control means for controlling the operation of aswitch. The present application is a continuation of my copendingapplication Serial No. 215,372 entitled, Switch Control Mechanism, filedMarch 13, 1951, now abandoned.

In certain arts, for example, any one of the automotive brake controlart or the stamping press art, it is desirable to control the time ofoperation of a brake mechanism in its operation of either maintaining acertain rnass static after said mass is brought to a stop or itsoperation of bringing said mass to a stop in which case the brakemechanism is applied while the mass is still in motion. it isaccordingly an object of my invention to effect this end and this may bedone by the provision of a simple, compact and easily serviced switchcontrolling electrical meansincluding a relay the switch of the relayserving as a part of the means being controlled, i.e., an anticreepmechanism of the brake system of an automotive vehicle. With thisadaptation of my invention there is provided means insuring an operationof the anti-creep mechanism either before or after the vehicle comes toa stop depending upon the adjustment of the mechanism; and an importantobject of my invention is to include, in this switch controlling means,a switch mechanism which is, without fail, operative to effect thedesired operation of the relay switch at a certain time just before thevehicle comes to a stop and at a certain time just after the movement ofthe vehicle is initiated.

Yet another object of my invention is to provide a switch controllingmechanism controlled by a control member, i.e., a vehicle speedresponsive governor operated switch, such that the switch to becontrolled may be operated either before a certain event, for example,at a certain time before said control member comes to a stop, or at acertain time after said event, for example, at a certain time after saidmember comes to a stop or after said member is started, or at the sameor substantially the same time as the happening of said event, forexample at the same or substantially the same time said member comes toa stop.

A further object of my invention is to provide, in an automotive vehicleincluding a four-wheel brake mechanism, brake anti-creep means,including a valve or its equivalent, for controlling the operation oftwo of the wheel brakes of the mechanism preferably the two frontbrakes; together with means, responsive to the speed of rotation of twoof the wheels preferably the two rear wheels of the vehicle, forcontrolling said valve.

A further object of my invention is to provide, in a four-wheelhydraulic brake system including a brake anticreep mechanism, poweroperated time control means for controlling the operation of a controlmember of the anti-creep mechanism said time control mechanism includinga power operated switch and means for controlling the operation of saidswitch including a time delay relay and means for controlling theoperation of the coil of said relay; and another object of my inventionis to include, in said latter control means, a plurality of sources ofelectricity such as a plurality of condensors, one of said sourcesacting as a means for storing electrical energy and serving to energizethe relay coil and the second of said sources serving, in the main, toenergize the latter source of electricity; and a further object of myinvention is to provide intermittently operable means for energizing theaforementioned second source of electricity. An important feature of myinvention is to so control the operation of this anti-creep mechanismthat the same is, with a certain operation of the accelerator,ineffective to hold the brakes applied, that is inoperative for itsintended purpose, in the operation of getting the vehicle under way andwhen the vehicle is traveling below a certain relatively low criticalspeed. With such a control the driver will not be handicapped by havingan undesired holding of the brakes when operating the vehicle near astop and go traffic sign.

A further object of my invention is to provide, in an automotivevehicle, a brake anti-creep mechanism which is operative to effect a.holding of the brakes at or below a certain vehicle speed and with acertain operation of the accelerator, said holding operation beingeffected when the vehicle is being either accelerated or deceleratedbeiow said certain speed.

The above and other objects and features of the invention will appearmore fully hereinafter from a considera tion of the followingdescription taken in connection with the accompanying drawings where oneembodiment of the invention is illustrated by way of example.

Figure 1 is a diagrammatic view disclosing one embodiment of myinvention employed as a part of the anticreep mechanism of an automotivevehicle;

Figure 2 discloses the electrical hookup of the mechanism of Figure l;and

Figure 3 is a sectional view disclosing details of the solenoid operatedcheck valve of the mechanism of Figure 1. I

There is disclosed in Figures 1 and 2 a preferred embodiment of myinvention wherein my switch controlling mechanism is employed to controla well known type of brake mechanism of an automotive vehicle saidmechanism including a well known type of anti-creep mechanism. Thisbrake and anti-creep mechanism, no claim to which is made, includes amaster cylinder 10 housing a piston, not shown, which is actuated as aresult of the manual operation of a brake pedal 12. Depression of thebrake pedal to apply the brakes energizes slave cylinders 14 which inturn actuate the brake shoes 16 of the wheel brakes of the vehicle. Inthis operation an incompressible or substantially incompressible brakefluid flows through conduits 18 and upon release of the brake pedal acertain mechanism including return springs, not shown, operates toreturn the parts of the mechanism to their brake oflf positions.

Briefly describing the anti-creep mechanism of the well known brakemechanism, a solenoid operated check valve 20, Figure 3, preferablyinserted in the system to control the front brakes of the vehicle,operates, with a release of the brake pedal and after the energizationof a grounded solenoid 22, to hold a predetermined back pressure againstthe slave cylinders, and thereby maintain a predetermined amount ofbraking eliort on the front wheels of the automotive vehicle; however,said solenoid when deenergized serves to disable this vdve and therebydisable the anti-creep mechanism. Describing the latter operation aspring loaded yieldable member 24, housed within the armature 26 of thesolenoid, is normally spaced from an opening 28 in the pole piece 30 ofthe solenoid thereby making it possible for the brake fluid to freelyreturn Patented Mar. 8, 1960 heavens through an opening 32 in the checkvalve, the opening 28, and thence through a recess 34 in the armature 26which recess extends into communication with the front face of theyieldable valve closure member 24, and on toward the master cylinder 19.The pole piece is provided with an annular seat surrounding the opening28 which projects rearwardly of the remaining portion of the pole piece,to permit a predetermined amount of yielding of the spring loadedyieldable memebr 24 before the armature 26 contacts the pole piece 30.Surrounding opening 2% in the pole piece 3% are a plurality of openings60 (twoof which are shown in section) which will at all times permitforward fluid how to the wheel cylinders 14. The check valve 20 isprovided with a rubber coating which covers these openings at}preventing return flow through these openings. All of the return flow,therefore, passes through opening 28; and when the solenoid 22 isenergized, its closure member 24 is biased against the opening 28 with apredetermined force. If the brakes have been applied when the solenoid22 is actuated, a predetermined back pressure will be held in the wheelcylinders 1l-any excess over and above this predetermined amount beingrelieved past the closure member 24.

In certain cars of the day the solenoid 22 is energized andde-energized, to operate the anti-creep portion of the brake mechanism,with an operation of a vehicle speed responsive governor operatedswitch; however this governor is somewhat uncertain in operationparticularly as to its time of operation. Accordingly, it is theprincipal object of my invention to provide an efficient and effectivemeans for controlling the time of operation of a switch mechanism, andsaid control means may, as indicated by an inspection of Figures 1 and2, be substituted for the aforementioned vehicle speed responsivegovernor operated control switch of the anti-creep mech anism of theday.

Describing now the switch control means of Figures 1 and 2 there isprovided a normally closed switch 34 of a solenoid operated relay 36;and this switch is preferably biased to its closed position by a spring38. The solenoid coil 40 of the relay is electrically connected inseries with a grounded battery 42, the ignition switch 44 of thevehicle, and an insulated contact 46 of a vehicle speed responsivesingle pole double throw governor switch 43 no claim to which is made.The common arm 50 of the switch 43, shown in its neutral position inFigure 2, is electrically connected in series with a condenser 52 ofrelatively low capacity, say 500 mfd, the ignition switch 44 and thebattery 42; and an insulated contact 54 of the switch 48 is grounded at55. The arm 50 of the switch 48 is preferably driven by cam meansconnected with the propeller shaft of the vehicle; accordingly thegovernor switch 48 is operative in accordance with the speed of thevehicle. Numerous cam arrangements can be made to operate the switch,one such arrangement may include a spring 59 to bias the pole in onedirection, and a cam 37 to force the pole in the opposite direction,thereby causing the pole to alternately engage its opposite contacts.The normally closed relay switch 34 is electrically connected in serieswith the solenoid 22, a grounded accelerator operated breaker switch 53which is closed when the accelerator is released, the ignition switch44, and the grounded battery 42. Describing now one of the principalfeatures of my invention, a condenser 56 of a high capacity, say 1500mfd, is electrically connected in parallel with the relay coil 4d; and agrounded accelerator operated switch 58 completes the electricalcontrols of my inventionsaid switch being electrically connected inseries with the coil 46 and ignition switch 44- and being closed whenthe accelerator is depressed a relatively small amount. The relay 36 andcondensers 52 and 56 may be housed within one container indicated by thereference numeral 51 in Figure l.

Describing now in brief an operation of the embodiment of my inventiondisclosed in Figures 1 and 2, the mechanism is preferably so adjustedthat the anti-creep mechanism is brought into play just before the caris stopped, that is during the so-called feathering operation of thebrakes. Explaining this operation it is to be noted that the relayswitch 34 is held open by an operation of the relay coil 40 said coilbeing energized by virtue of the discharging operation of the condensers52 and 51), particularly the latter; and as set forth below, thecondenser 56 is charged to maintain its voltage by the operation of thecondenser 52. The rate of discharge of the condenser 56 and theresultant timing of operation of the switch 34 to render the anti-creepmechanism effec tive, may be controlled by a rheostat, not shown,connected in series with the contact 46 and switch 44 and by-passing therelay coil 40.

When the vehicle is placed in motion, the vehicle speed responsivebreaker switch 48 immediately operates to charge the condenser 52 andthis results, with a movement of the arm 50 of the switch 48 intocontact with the contact 46, in a charging of the condenser 56 to effectan energization of the coil 4%. The condenser 56 reaches its full chargewhen the speed of the vehicle is increased to a certain factor, say fivemiles per hour. Thereafter condenser 56 operates to maintain theenergization of the coil 4% accordingly, the switch 34 is opened therebyrendering the anti-creep mechanism inoperative; however, when the speedof the car is reduced sufficiently to make the rate of discharge of thecondenser 56 exceed the rate of charge thereof then there comes a time,preferably a very short time before the car comes to a stop say when thevehicle is traveling at two miles per hour, when the condenser 56 isdischarged sufiiciently to reduce the voltage across the relay coil 40below its drop out value. The switch 34 is then automatically closed bythe operation of the spring 38 thereby initiating an operation of theanti-creep mechanism. The relay coil 49 and condenser 56 are preferablywired in parallel in order to hold the relay energized during the halfcycle of the breaker switch 48 in which the common arm 50 of the switchis in contact with the grounded side. In other words the common arm ofthe breaker switch shuttles electrical energy from the battery 42 to therelay 36, the condenser 56 serving to hold the relay energized whilemaking the exchange. The condenser 56 is used to store the excess energyover that required by the relay coil.

Inasmuch as applicant uses a condenser arrangement for feeding directcurrent to the relay coil .9, the vehicle may be stopped in a positionwherein the switch arm 50 remains in contact-either with the contact 54or the contact 46 without shorting out the battery. Prior art deviceshave necessitated switch structures which could not remain closedregardless of the position in which the vehicle was stopped. Applicantsswitch structure 38 can therefore be much'simpler and more inexpensiveto manufacture than are the normally open switches which have been usedheretofore in other types of no creep systems.

A further refinement of applicants invention is to be found in the useof the accelerator operated switch 53, which switch is intended toenergize the coil 40 whenever the accelerator pedal is moved out of itsclosed position. It is a property of relay coils generally that a largerflow of electrical energy is required through the coil to move itsarmature (or in this case the switch blade 34) from its remote positionto its position engaging the core of the armature, than is required tohold the armature (or in this case the switch blade 34) in engagementwith the core of the solenoid once it is so positioned. Without the useof the switch 53, a highervehicle speed would be required to initiallyproduce an opening of the switch 34, than is required to permit theswitch blade 34 to separate from the relay coil 48 and close the switch34. As for example, one form of relay 36 which has been used without theswitch 58 required the vehicle to be accelerated to a speed of aboveapproximately 5 miles per seams hour inorder to open the switch 34;while deceleration of the vehicle below approximately 2 miles per hourwas necess'arybefore the switch 34 would again close. Without the switch58 therefore, there was a range of vehicle speeds of from 2 to 5 milesper hour during which the no creep system may or may not be in operationdepending upon whether the vehicle had been accelerated or deceleratedto within this range.

By the use of the switch 58, the above mentioned range of from2 to 5miles per hour was eliminated so that the no creep system was alwaysoperable when the vehicle was moving above approximately 2 miles perhour. Referring to Figure 2 of the drawing it will be seen that anactuation of the accelerator pedal immediately causes the switch blade34 to be opened such that the switch 34 will be held open by'the speedresponsive switch 48 whenever the vehicle is travelling above the lowerlimit, which in the above example was approximately 2 miles per hour.Switch 58 therefore assures that the no creep system will be disabledwhenever a vehicle speed above a predetermined velocity is reached; andpermits the operator to take his foot off of the accelerator pedal andapply the brakes in the range of from 2 to 5 miles per hour, such as mayoccur during a parking operation, without the brakes being held applied.

There is thus provideda simple, compact, and efficient time controlmeans for controlling the operation of a brake anti-creep mechanism. Thecondenser 56 provides means for storing electrical power utilized tooperate the anti-creep mechanism; and the condenser 52, by its operationof charging the condenser 56, insures an operation of the latter bymaintaining a voltage across the relay coil above its drop out value.The operation of the condenser 52 may be likened unto the operation of apump and the operation of the condenser 56 may be likened unto theoperation of a storage tank in the operation of the mechanism of myinvention. Described in other words the switch operating power means ofmy invention includes a motor such as the coil, that is electric motor40 of the relay 36, means for energizing the motor including a source ofpower, that is the battery 42, a means for storing electricity flowingfrom the battery, that is the condenser 52, means for controlling thesource of power such as the intermittently operated breaker switch 48,and means, such as the condenser 56, controlled by the breakor switchand operable to store electricity flowing from the condenser 52 saidstoring means being activated by the condenser 52 and operable as theprincipal means for energizing the motor. The accelerator operatedswitch 58 in cooperation with other parts of the mechanism including thebattery 42, provide means for disabling the brake anti-creep mechanismwhen said switch is closed thereby insuring the desired operation of thebrakes when the vehicle is being maneuvered in the vicinity of thetraflic controls of the day.

The time of operation of the anti-creep mechanism with respect to themovement of the vehicle, that is the determination of whether or not theanti-creep mechanism comes into play before or after the car comes to astop and when this'operation is effected, may be controlled by adetermination of any one or a plurality of many factors including thecapacity of the condensers, the air gap of the relay 36, the resistanceof the relay coil 40, the strength of the spring 38 and the speed ofoperation of the breaker switch 48. The latter may include a cam foroperating the movable contact of the switch, accordingly the operationof the switch may be controlled by the number, size and position of thelobes on said cam.

The relay switch 34, that is the switch which is controlled, may also beemployed in other arts; for example said switch may be employed tocontrol the closure of the doors of an automotive bus and to control theoperation of a transmission operating mechanism of an auto motivevehicle to effect say a low gear setting of said mechanism; and toeffect the latter operation of my invention the parts of the mechanismare preferably so con structed as to effect a closure of the switch 34 ashort time prior to a stopping of the vehicle.

The switch control means of my invention also finds a place when used inan automotive vehicle including a fluid coupling combined with the abovedescribed hydraulic and anti-creep brake mechanism; and my invention mayalso 'be incorporated in the brake mechanism of a stamping press whereinit is desirable to employ a small inexpensive brake to maintain arelatively massive fly wheel or equivalent part of the press mechanismstatic. With the mechanism of my invention the brake is applied to thefly wheel of the stamping press after and only after said fly wheel hascome to a stop; or the parts may be constructed and adjusted so that thebrake is applied just before the fly wheel comes to a stop.

I claim:

1. In an automotive vehicle having a brake and an accelerator, a fluidpressure motor device for operating a brake on the vehicle, a pressureproducing device, flow conducting means establishing fluid flowcommunication between said devices, an electrically controlled valve insaid flow conducting means for restricting back flow from said fluidpressure motor to said pressure producing device When energized,normally closed solenoid operated switch means for energizing saidvalve, a single pole double throw switch the contacts of which areconnected in the electrical supply circuit for the solenoid of saidsolenoid operated switch means, a first condenser in parallel circuitwith respect to said solenoid, a second condenser connected between thepole of said single pole switch and the side of. said first condenseropposite said switch, cam means for causing said pole of said switch tooscillate between its contacts, means for causing said cam means torotate at a speed which increases with vehicle speed, spring means forcausing said pole to follow the contour of said cam means, and switchmeans connected to said solenoid for deenergizing said solenoid upondepressing said accelerator.

2. In a speed control system for a movable device: a control mechanismhaving a normal position and a second position in which it performs aspeed regulating function for said movable device, electrical controlmeans of generally predetermined impedance causing said controlmechanism to be held in its second position when an electrical flowabove a generally predetermined rate passes therethrough and whichcauses said control mechanism to be in its normal position when saidelectrical flow rate decreases below said generally predetermined rate,a first electrical condenser connected to said electrical control meansin such manner that a charge on said condenser decays through saidelectrical control means, a single pole double throw switch having twocontacts between which the pole oscillates, an electrical supply circuitfor said first condenser and connected in series with said contacts ofsaid single pole switch, a second condenser one side of which isconnected to the side of said first condenser opposite said contacts andthe other side of said second condenser being connected to said pole ofsaid single pole switch, rotary means for oscillating said pole piecebetween said contacts, and means rotating said rotary means generallyproportional to the speed of said movable device, whereby said controlmechanism is moved into its second position at a generally predeterminedspeed of said movable device.

3. In a speed control system for a movabledevice: a control mechanismhaving a normal position and a second position in which it performs aspeed regulating function for said movable device, electrical controlmeans including an actuating solenoid of generally predeterminedimpedance causing said control mechanism to be held in its secondposition when an electrical flow above a generally predetermined ratepasses therethrough and which causes said control mechanism to be in itsnormal position when said electrical flow rate decreases below saidgenerally predeterminedrate, a first electrical condenser connected tosaid solenoid in such manner that a charge on said condenser decaysthrough said solenoid, a single pole double throw switch having twocontacts between which the'pole oscillates, an electrical supply circuitfor said first condenser and connected in series with said contacts ofsaid single pole switch, a second condenser one side of which isconnected to the side of said first condenser opposite said contacts andthe other side of said second condenser being connected to said pole ofsaid single pole switch, rotary means for oscillating said pole piecebetween said contacts, and means rotating said rotary means generallyproportional to the speed of said movable device, whereby said controlmechanism is moved in to its second position at a generallypredetermined speed of said movable device.

4. In a braking system for a rotatable mechanism: a brake for stoppingrotation of the mechanism, electrical control means of generallypredetermined impedance causing said brake to be held applied when anelectrical flow below a generally predetermined rate passes through thecontrol means and which causes the brake to be released when saidelectrical flow rate increases above said generally predetermined rate,a first electrical condenser connected to said electrical control meansin such manner that a charge on said condenser decays through saidelectrical control means, an electrical supply circuit, a secondcondenser, cyclic switch means which when in one part of its cycleconnects said second condenser to said electrical supply circuit andwhich in another part of its cycle is connected to said second condenserin a manner permitting a charge on said second condenser to betransferred to said first condenser, drive means cycling said cyclicswitch means at a rate proportional to the speed of rotation of saidrotatable mechanism, an accelerator lever having a normal position outof which said lever is moved to increase the speed of rotation of saidrotatable mechanism, and means disabling said electrical control meansfrom holding said brake applied when said accelerator lever is moved outof its normal position 5. In a braking system for a rotatable mechanism:a brake for stopping rotation of the mechanism, electrical control meansof generally predetermined impedance causing said brake to be heldapplied when an electrical flow below a generally predetermined ratepasses through the control means and which causes the brake to bereleased when said electrical flow rate increases above said generallypredetermined rate, a first electrical condenser connected to saidelectrical control means in such manner that a charge on said condenserdecays through said electrical control means, a single pole double throwswitch having two contacts between which the pole oscillates, anelectrical supply circuit for said first condenser and connected inseries with said contacts of said single pole switch, a second condenserone side of which is connected to the side of said first condenseropposite said contacts and the other side of said second condenser beingconnected to said pole of said single pole switch, rotary means foroscillating said pole between said contacts, means rotating said rotarymeans generally proportional to the speed of said mechanism, anaccelerator lever having a normal position out of which said lever ismoved to increase the speed of rotation of said rotatable mechanism, andmeans disabling said electrical control means from holding said brakeapplied when said accelerator lever is moved out of its normal position.

6. In a braking system for a rotatable mechanism: a brake for stoppingrotation of the mechanism, electrical control means of generallypredetermined impedance causing said brake to be held applied when anelectrical fiow below a generally predetermined rate passes through thecontrol means and which causes the brake to be released when saidelectrical fiow rate increases above said generally predetermined rate,a first electrical condenser connectedtosaid electrical-control means insuch manher that a charge on said condenser decays through saidelectrical control means, an electrical supply circuit, a secondcondenser, cyclic switch means which when in one part of its cycleconnects said second condenser to said electrical supply circuit andwhich in another part of its cycle is connected to said first condenserin a manner permitting a charge on said second condenser to be transferred to said first condenser, drive means cycling'said cyclic switchmeans at a rate generally proportional 'to the speed of rotation of saidrotatable mechanism, an accelerator lever having a normal position outof which said lever is moved to increase the speed of rotation of saidrotatable mechanism, means disabling said electrical control means fromholding said brake applied when said accelerator lever is moved out ofits normal position,

means producing an electrical flow rate through said electrical controlmeans greater than said generally predetermined rate when saidaccelerator is moved out of its normal position. a

7. in a braking system for a rotatable mechanism: a brake for stoppingrotation of the mechanism, electrical control means of generallypredetermined impedance causing said brake to be held applied when anelectrical flow below a generally predetermined rate passes through thecontrol means and which causes the brake to be released when saidelectrical flow rate increases above said generally predetermined rate,a first electrical condenser connected to said electrical control meansin such manher that a charge on said condenser decays through saidelectrical control means, a single pole double throw switch having twocontacts between which the pole oscil-v lates, an electrical supplycircuit for said first condenser and connected in series with saidcontacts of said single pole switch, a second condenser one side ofwhich is connected to the side of said first condenser opposite saidcontacts and the other side of said second condenser being connected tosaid pole of said single pole switch, rotary means for oscillating saidpole between said contacts, means rotating said rotary means generallyproportional to the speed of said mechanism, an accelerator lever havinga normal position out of which said lever is moved to increase the speedof rotation of said rotatable mechanism, means disabling said electricalcontrol means from holding said brake applied when said acceleratorlever is moved out of its normal position, and means producing anelectrical fiow rate through said electrical control means greater thansaid generally predetermined rate when said accelerator is moved out ofits normal position.

8. In a braking system for a rotatable mechanism: a brake for stoppingrotation of the mechanism, a relay switch having a coil of generallypredetermined impedance causing said brake to be held applied when anelectrical flow below a generally predetermined rate passes through saidcoil and which causes the brake to be released when said electrical flowrate increases above said generally predetermined rate, a firstelectrical condenser connected in parallel with respect to said coil sothat a charge on said condenser decays through said coil, a single poledouble throw switch having two contacts between which the poleoscillates, an electrical supply circuit for said first condenser andconnected in series with said coil and said contacts of said single poleswitch, a second condenser one side of which is connected to the side ofsaid first condenser opposite said contacts and the other side of saidsecond condenser being connected to said pole of said single poleswitch, rotary means for oscillating said pole between said contacts,means rotating said rotary means generally proportional to the speed ofsaid mechanism, an accelerator lever having a normal position out ofwhich said lever is moved to increase the speed of rotation of saidrotatable mechanism, means disabling said relay switch from holding saidbrake applied when said accelerator lever is moved out of its normalposition, and means producing an electrical fiow rate through said coilof said relay switch greater than 9. said generally predetermined ratewhen said accelerator is moved out of its normal position.

9. In a braking system for a rotatable mechanism: a brake for stoppingrotation of the mechanism, a relay switch having a coil of generallypredetermined impedance causing said brake to be held applied'when anelectrical flow below a generally predetermined rate passes through saidcoil and which causes the brake to be released when said electrical flowrate increases above said generally predetermined rate, a firstelectrical condenser connected in parallel with respect to said coil sothat a charge on said condenser decays through said coil, a single poledouble throw switch having two contacts between which the poleoscillates, an electrical supply circuit for said first condenser andconnected in series with said coil and said contacts of said single poleswitch, a secondcondenser one side of which is connected to the side ofsaid first condenser opposite said contacts and the other side of saidsecond condenser being connected to said pole of said single poleswitch, rotary means for oscillating said pole between said contacts,means rotating said rotary means generally proportional to the speed ofsaid mechanism, an accelerator lever having a normal position out ofwhich said lever is moved to increase the speed of rotation of saidrotatable mechanism, means disabling said relay switch from holding saidbrake applied when said accelerator lever is moved out of its normalposition, and switch means connected in series with said relay coil andsaid electrical supply circuit and which switch means is closed by saidaccelerator lever when moved out of its normal position to produce anelectrical flow rate through said relay coil above said generallypredetermined rate.

References Cited in the file of this patent UNITED STATES PATENTS Harmonet al. Jan. 22,

